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Werk
I am building a stand alone AQ unit for a friend but cannot get the LCD to display anything.
I have changed the display, (it works on another unit if i change the address in the software to suit) but not with the new build.
I have not installed the Tx socket or Tx unit and LED.
Code is attached
Regards
Jim

Code:

/***************************************************************************
WeatherDuino - Air Quality Monitor
For PMS7003 and MH-Z19B

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*************************************************************************************/

#if (LCD_Display == 1)
// ---- Define LCD I2C address
// Only change this if your LCD don't display any data. I2C_Scanner utility may help you to find the address of your LCD display
// Default address will work most of the times!
#define LCD_I2C_Address 0x20

// --------------------------------------------------------------------------------------
// SHT31 I2C Address - Default address will work most of the times!
// --------------------------------------------------------------------------------------
#define SHT31_address 0x44 // Default value is 0x44, but it can be changed to 0x45

If a particular LCD module works with one unit at a given address, it should work with any other unit using the the same I2C address.
Having or not the TX module installed doesn't affect the functionality of the LCD display.

If a particular LCD module works with one unit at a given address, it should work with any other unit using the the same I2C address.
Having or not the TX module installed doesn't affect the functionality of the LCD display.

Werk,
I understand the address issues but I could not get the system to boot.
I finally solved the issue, it was the HTU21D, I have no idea why but by disconnecting it the unit boots as it should and I replaced it with a spare and now all is working well.
On the issue of 20 x4 LCD’s I recently received a couple of serial units without the I2C module, and realising my mistake, I ordered the modules and attached them but they will not work with my AQ unit.
I noticed that the only difference is that the two capacitors C1 andC2 are missing from the two ex serial modules.
Do you know what the values of these SMD caps are? C2 appears to be a tantalum as it has a polarity marking, because I am sure that if fitted they would be usable again
Regards
Jim

(13-02-2018, 22:15)[Barrow4491 Wrote: On the issue of 20 x4 LCD’s I recently received a couple of serial units without the I2C module, and realising my mistake, I ordered the modules and attached them but they will not work with my AQ unit.
I noticed that the only difference is that the two capacitors C1 andC2 are missing from the two ex serial modules.
Do you know what the values of these SMD caps are? C2 appears to be a tantalum as it has a polarity marking, because I am sure that if fitted they would be usable again

Hi Jim,

Do not fully understand what you are dealing with serial modules? I'm used to buying both parts separately, and after soldering I've never experienced any problems.
For example on Aliexpress:

I also order i2c modules separately and solder them. It is necessary to make bridges of welds on A0 A1 and A2 to define the address, after the address does not correspond to what one can find on internet. Just use an I2c address scan provided with the weatherduino software package.
So just change the address in the INO RX.

[attachment=1317 Wrote:Werk_AG pid='8888' dateline='1518633182']Usually I don't do any bridges at A0, A1 or A2. Without any bridges, the I2C address is 0x27 (at least for all the back pack modules I have seen), which is the default address defined on the software.

Werk,
As mentioned i have an issue with two 20 x 4 LCD displays.
The top one in the photo was purchased as an I2C compatible device and works well with the address of 0x3F (chip is PCF 8574AT).
The lower one is one of two purchased as serial models and I attached the I2C boards myself, both have the same 8574AT chip but neither will work regardless of address used.
The only difference appears to be that the non working boards do not have capacitors C1 and C2 fitted
Any ideas?
Jim